1. Field of the Invention
The present invention relates to a high-speed finely pulverizing method employed for generating reduced pressure jet stream and the equipment therefor.
2. Discussion of the Background
Conventional pulverizers adopting a mill principle generate heat due to the thermal conversion of energies such as those of compression, shear and rolling friction generating in the pulverizing process, when finely pulverizing materials containing high lipid, high moisture, high protein, or a high amount of saccharide or special enzyme, resulting in very difficult fine pulverization due to sticking caused by bleeding of lipid, adherence caused by moisture, burning caused by oxidizing metamorphosis etc., film formation, and the like.
Moreover, since heat generation is proportional to the number of revolutions, a low speed is used without exception in order to suppress heat generation.
Showing a typical example using stone mortar, 156 rpm is used for traditional goods such as ground tea (Uji Tea Research Laboratory), leading to extremely low capacity (40 g-100 g/h). Hence, 1,000 stone mortars are working at same factory.
Furthermore, there is a compressive pulverization system using rolls as a low-speed fine pulverizer. This is superior for the pulverization at ambient temperature, but the capacity is very low because of low speed, hence the operation required increased cost and was difficult economically to be utilized.
Now, a lot of powder-producing machines have been used so far in various industrial sectors. As a representative of super colloid mill being one example thereamong, there is Mass Colloider (trade name) that efficiently provides super fine powder of hard pulverizing materials. This is constituted by a fixed top grindstone having a flat grinding area at an outer circumference, the width thereof being freely adjustable, and a rotating bottom grindstone having flat grinding area similarly at outer circumference and being rotatable at high speed, arranged so that their flat grinding areas are in opposition one another, and the pulverizing material fed between these grindstones from a central opening of the fixed grindstone is super finely pulverized by means of overall actions of centrifugal force, impact grinding force, shear force, etc. caused between said opposed flat grinding areas.
The life of such super colloid mail and Mass Colloider lies in the built-in grindstones.
In particular, with hard pulverizing materials, that is, materials containing high lipid, high moisture, high protein, or a high amount of saccharide or special enzyme, the lipid, moisture, protein and enzyme peculiar to pulverizing materials adhere, stick, burn or form a film due to heat of friction to vary the physical properties, thus having made it impossible to be commercialized as powders. For avoiding these, if widening the clearance between grindstones occurs, then the transmutation phenomenon due to heat generation may be improved slightly, but fine pulverization is impossible. Reduction of the number of revolutions of the grindstone may improve this to some extent, but stable operation is impossible together with decreased capacity. Also, if the aperture of grindstones is increased, then the peripheral speed of grindstone increases even at low-speed revolutions, leading to subtle changes in heat generation, adherence, sticking, burning, film formation, etc.
Based on conventional concepts, it has been considered that the number of revolutions and the peripheral speed have the same implication because of proportionality between the number of revolutions and the peripheral speed. During repeated tests, however, it has been found that, when the number of revolutions and the peripheral speed exceed certain lines, a change for the better is seen suddenly in the pulverizing capacity.
Increasing the peripheral speed further, it has been found that a large capacity can be exerted almost without raising the temperature even for the extremely hard pulverizing materials that have been hitherto considered to be quite impossible.
As a result of having repeated the tests varying the number of revolutions variously with respective grindstones, a remarkable change in powdering of hard pulverizing materials was recognized at a peripheral speed of over 1850 m/min, preferably over 2200 m/min in all cases, as shown in Table 1.
TABLE 1 ______________________________________ Diameter of Number of Peripheral grindstone revolutions, speed, No .phi., mm rpm m/min Remarks ______________________________________ 1 150 5000 2350 Good powder for hard pulverizing materials Overheating of motor 2 240 3000 2250 Best current value, capacity and material temperature (Best safety and machine cost) 3 360 2000 2260 Good 4 500 1450 2276 Good Difficulty in machine cost 5 750 1000 2360 Good Difficulty in machine cost 1450 3422 Safety? ______________________________________
Moreover, when attempting to classify the powder obtained particularly by dry pulverization with said super colloid mill, clogging is liable to occur, if using a usual air classifier with screen, thus having posed a problem in installing an automatic production line for powder.